A seat lifter apparatus that is capable of adjusting a position of a seat for a vehicle in an up-down direction generally includes a link mechanism supporting the seat at an upper side of the link mechanism via link members which are rotatably provided. In many cases, a sector gear is provided at any of the link members in a state sharing a rotation shaft with the aforementioned link member to integrally rotate therewith. The link member rotates on a basis of a driving force transmitted via the sector gear so that the seat which is supported at the upper side of the link mechanism is configured to move upward and downward.
For example, a seat lifter apparatus disclosed in Patent document 1 includes a pinion gear meshed with a sector gear and an operation handle coaxially provided at the pinion gear. In addition, a rotation control apparatus including two clutch portions which are coaxially arranged side by side is disposed between the pinion gear and the operation handle. Because of the rotation control apparatus, the pinion gear is driven to rotate on a basis of a reciprocating rotation which is input to the operation handle and a rotation position of the pinion gear is configured to be maintained.